Retinoic acid (RA) plays a fundamental role in diverse cellular activities. Cellular RA binding proteins (CRABPs) are thought to act by modulating the amount of RA available to nuclear RA receptors. CRABPs and cellular retinol-binding proteins (CRBPs) share a unique fold of two orthogonal beta-sheets that encapsulate their ligands. It has been suggested that a trio of residues are the prime determinants defining the high specificity of CRBPs and CRABPs for their physiological ligands.

Crystallographic Studies on a Family of Lipophilic Transport Proteins. Refinement of P2 Myelin Protein and the Structure Determination and Refinement of Cellular Retinol-Binding Protein in Complex with All-Trans-RetinolCowan, S.W.,Newcomer, M.E.,Jones, T.A.(1993) J.Mol.Biol.&nbsp230: 1225